Aminoisophthalate Bridged Cd(II)-2D Coordination Polymer: Structure Description, Selective Detection of Pd 2+ in Aqueous Medium, and Fabrication of Schottky Diode.

Photoluminescence activity of coordination polymers (CPs) has evoked intricate applications in the field of materials science, especially sensing of ions/molecules. In the present study, 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 5-aminoisophthalate (HAIPA ^- ) coordinated to Cd(II) to architect a coordination polymer, {[Cd(HAIPA)(tppz)(OH)]·3H ₂ O} _n (CP 1 ) which unveils blue emission in an aqueous acetonitrile (98% aqueous) suspension. The emission is selectively quenched by Pd ²⁺ only without interference in the presence of as many as 16 other cations. The structure of CP 1 shows the presence of a free -COOH group, and the interlayer (-CO)O(2)···O(7) (OC-) distance, 4.242 Å, along with the π···π interactions (3.990, 3.927 Å), may make a cavity which suitably accommodates only Pd ²⁺ (van der Waal's radius, 1.7 Å) through the Pd(II)-carboxylato (-COO-Pd) coordination. The stability of the composite, [CP 1 + Pd ²⁺ ] may be assessed from the fluorescence quenching experiment, and the Stern-Volmer constant ( K _SV ) is 7.2 × 10 ⁴ M ^-1 . Therefore, the compound, CP 1 , is a promising sensor for Pd(II) in a selective manner with limit of detection (LOD), 0.08 μM. The XPS spectra of CP 1 and [CP 1 + Pd ²⁺ ] have proven the presence of Pd ²⁺ in the host and the existence of a coordinated -COO-Pd bond. Interestingly, inclusion of Pd ²⁺ in CP 1 decreases the band gap from 3.61 eV (CP 1 ) to 3.05 eV ([CP 1 + Pd ²⁺ ]) which lies in the semiconducting region and has exhibited improved electrical conductivity from 7.42 × 10 ^-5 (CP 1 ) to 1.20 × 10 ^-4 S m ^-1 ([CP 1 + Pd ²⁺ ]). Upon light irradiation, the electrical conductivities are enhanced to 1.45 × 10 ^-4 S m ^-1 (CP 1 ) and 3.81 × 10 ^-4 S m ^-1 ([CP 1 + Pd ²⁺ ]); which validates the highly desired photoresponsive device applications. Therefore, such type of materials may serve as SDG-army (sustainable development goal) to battle against the environmental issues and energy crisis.